This application claims the priority of Korean Patent Application Nos. 2003-64207 and 2004-18284 filed in the Korean Intellectual Property Office on Sep. 16, 2003, and Mar. 18, 2004, respectively, and U.S. Provisional Patent Application No. 60/477,035 filed in the United States Patent and Trademark Office on Jun. 10, 2003, the disclosures of which are incorporated herein in their entirety by reference.
1. Field of the Invention
Apparatuses consistent with the present invention relate to a compact light source module and a projection display adopting the compact light source module and, more particularly, to a compact light source module using a light source such as a light emitting diode and a projection display adopting the compact light source module.
2. Description of the Related Art
FIG. 1 shows the structure of a conventional projection display. Referring to FIG. 1, the conventional projection display includes liquid crystal display (LCD) panels 20R, 20G, and 20B which are optical modulators, an illumination unit 10 which irradiates light onto the LCD panels 20R, 20G, and 20B, and a projection lens 40 which magnifies and projects a modulated image.
The LCD panels 20R, 20G, and 20B modulate red (R), green (G), and blue (B) beams, respectively, to be suitable for respective image data so as to display a color image. Reference numeral 30 denotes a synthesizing prism which combines the modulated R, G, and B beams and then irradiates the combined beam onto the projection lens 40.
The illumination unit 10 includes a light source 1, an integrator 3, a condenser lens 4, a plurality of mirrors 5R, 5G, and 5B, and a plurality of relay lenses 7 and 8.
The light source 1 may be a metal halide lamp or a super-high voltage mercury lamp and is located at a focal point of a reflective mirror 2 with a parabolic surface. The integrator 3 is used to irradiate a uniform beam onto the LCD panels 20R, 20G, and 20B and generally made of two fly-eye lenses in which micro-lenses are two-dimensionally arrayed. A light beam, which has passed through the integrator 3, is condensed by the condenser lens 4. The mirrors 5R, 5G, and 5B are selective reflector mirrors which reflect the R, G, and B beams, respectively, and transmit other color beams. A light beam is split into the R, G, and B beams via the mirrors 5R, 5G, and 5B, respectively, and then the R, G, and B beams are incident on the LCD panels 20R, 20G, and 20B, respectively, through the relay lenses 7 and 8. The LCD panels 20R, 20G, and 20B modulate the R, G, and B beams, respectively, so as to output R, G, and B color images. The synthesizing prism 30 combines the R, G, and B beams output from the LCD panels 20R, 20G, and 20B into one, and then the projection lens 40 magnifies and projects the combined beam.
However, in such a conventional projection display, a lamp is used as a light source to illuminate optical modulators and has a short life span. Therefore, when the conventional projection display is used at homes, the lamp should be frequently replaced with new one. Also, the light source is a large size. In order to solve these problems, studies on the use of compact light sources such as a light emitting diode (LED) with a relatively long life span, etc. are in progress. Japanese Patent Publication No. JP 2001-42431 discloses a projection device using an LED.
FIG. 2 shows the LED structure of a Luxeon Emitter manufactured by LUMILEDS Company. Referring to FIG. 2, a dome lens 62 as one of primary optics is installed over an LED chip 61. The dome lens 62 condenses a light beam emitted from LED chip 61.
The light beam, which has passed through the dome lens 62, has a light intensity distribution as denoted by reference character C1 or C2 of FIG. 3. In a graph of FIG. 3, the widthwise axis denotes a radiation angle and the lengthwise axis denotes a relative intensity of light. The light intensity distributions C1 and C2 are wing-shaped and gently dome-shaped, respectively, within the radiation angle between 0° and ±90°. However, the radiation angle should be between 0° and ±15° to illuminate the optical modulators 20R, 20G, and 20B. Therefore, a light beam with a light intensity distribution above the radiation angle between 0° and ±15°, i.e., a portion of the light beam with the light intensity distribution C1 or C2 above the radiation angle between 0° and ±15°, fails to illuminate the optical modulators 20R, 20G, and 20B and thus is lost. As a result, light efficiency deteriorates.
To prevent such loss of light, the conventional projection display includes secondary optics which condenses a light beam emitted from an LED before irradiating the light beam onto the optical modulators 20R, 20G, and 20B so that the light beam has a light intensity distribution as denoted by reference character C3 of FIG. 3. As a result, the additional use of the secondary optics makes an illumination system of the conventional projection display complicated and increases cost of manufacturing the illumination system.
In general, an LED emits a smaller amount of light than a metal halide lamp or a super-high voltage mercury lamp. Thus, the conventional projection display uses an array of LEDs as a light source. In this case, secondary optics is necessary. However, since the secondary optics has to be lenses, light condensing efficiency deteriorates. This will be explained in more detail with reference to FIGS. 4A and 4B.
In a paraxial area, the product of the size and angle of an image is conserved. Thus, the product of the emission area of an LED and the steradian of the emission angle of the LED is a conservation value which is called an “etendue”. When the etendue is less than the product of the area of a LCD panel and a steradian calculated from an F value of a projection lens, the light condensing efficiency increases.
As shown in FIG. 4A, when one LED is used, the product of the emission area ΦL and the steradian UL of the LED may be equal to the product of the emission area ΦL and the steradian UP of the LCD panel.
As shown in FIG. 4B, when an array of LEDs is used, the emission area ΣΦL of the array of LEDs is larger than the emission area ΦL of the LED of FIG. 4A. Here, the steradian UL of the emission angle of the array of LEDs is equal to the steradian UL of the LED of FIG. 4A, and the emission area ΦP of an LCD panel is equal to the emission area ΦL of the LCD panel of FIG. 4A. Therefore, in order to conserve the etendue, the steradian UP′ of the emission angle of the LCD panel of FIG. 4B is larger than the steradian UP of the LCD panel of FIG. 4A. Accordingly, when the array of LEDs as shown in FIG. 4B is used, light is lost, resulting in decreasing light condensing efficiency and the luminance of the projection display.